Speed of a mobile unit in a communications network may relate to the rate of wireless mobile channel variations. Consequently, one may wish to be able to obtain estimates of the speed of a mobile unit, in order to aid such functions as, for example, handoff, adaptive modulation, adaptive equalization, power control, etc.
Speed estimation may be done based on signals received at the mobile unit and/or at a base station or other fixed station of a network. However, received signals are generally corrupted by noise, fading, and the like.
Speed estimation, or equivalently, Doppler frequency estimation (i.e., because Doppler frequency is proportional to speed) may employ, for example, crossing-based methods or covariance-based methods. However, the accuracy of such estimates may tend to drop with increasing amounts of noise, interference, fading, etc. Furthermore, such estimators tend to be complex to implement and generally require the use of pilot symbols and/or signals.
Accurate estimation of the mobile speed which reflects the rate of wireless mobile channel variations is important for many applications such as handoff, adaptive modulation and equalization, power control, etc. Almost all background art methods for speed estimation are based on transmitted pilot tones.